The invention relates to a telecommunication network, a method of controlling such network and to a component of such network.
In order to establish communications between subscribers, a telecommunication network comprises several kinds of multiplexers in series. Generally, the first multiplexer which is connected to the network is called a switching node (SN) and the multiplexer which is the closest to a subscriber is called an access node (AN). An access node may be also connected to a switching node through another multiplexer which will be called here a subswitching node or subscriber-switching node.
The switching node and subswitching node are generally controlled by the network operator. The access nodes are located in subscribers' installations; they are generally owned or leased by subscribers. As access nodes and subswitching nodes are sold or leased in great numbers, it is preferable that their cost be limited, i.e. that they be realized with the greatest simplicity; in order to achieve this goal, the most complex control means are installed in the switching node.
For this purpose, the VB5.1 ETSI standard recommends the following network structure: each user or subscriber is connected through an access node or a subswitching node to a switching node via virtual paths (VP). A virtual path comprises generally several virtual channels (VC). A given bandwidth (i.e. a given bit rate) is allocated to each virtual path; this bandwidth may have different values in the upward and the downward directions. The upward direction is from the user to the network and the downward direction is from the network to the user; the downward direction needs generally more bandwidth than the upward direction. In fact, in the upward direction, simple requests are sent and in the downward direction important files are generally sent.
For instance, 8 Mbits/sec. is allocated to the downward direction (from the switching node to the subscriber node) and 800 Kbits/sec. is allocated to the upward direction (from the access node to the switching node).
If, with this VB5.1 standard, the total bandwidth is (downward) 8 Mbits/sec. between the switching node and the subscriber node and if there are 8 VP, each one has a bandwidth of 1 Mbit/sec., if the resources are distributed equally.
Therefore, the subscriber node (access and/or subswitching node) is very simple because it does not comprise any control means for controlling the connection and the bandwidth. However, this simplicity has the drawback that it is not possible to allocate temporarily more bandwidth to a VP, i.e. to a user.
When a user has the possibility to transmit and receive data with different qualities of service (QOS), i.e. with different priorities, one or several virtual channels VC is allocated to each quality of service. In that case, the corresponding virtual path must be provided with control means, generally called “shaping control means”, which take into account the bandwidth of each virtual channel in order to limit the total bandwidth of the virtual path to the bandwidth which is allocated to this virtual path. The shaping control means are expensive. Therefore, the goal of simplicity and low cost for the users' equipment is no more achieved.
In order to allocate dynamically the bandwidth to each VC, it is possible to use another ETSI standard named VB5.2. But the drawback of this technology is that the access node or subswitching node is complex and, therefore, more expensive. In fact, in this standard, the access or subswitching node controls dynamically the up and down connections and may provide instantaneously the requested bandwidth to each VC under the control of call control means provided in the switching node. It can be easily understood that the high cost stems from the fact that, for such call processing in the access node or subswitching node, it is necessary to use important memory means and processing power.
In the network according to the invention, the access node or subswitching node is almost as simple as in the VB5.1 standard but provides the possibility to allocate dynamically the bandwidth to each VP.
The invention takes advantage of the asymmetrical character of the traffic.
The network according to the invention is characterized in that, in the downward direction, the bandwidth allocated to each virtual path is variable under the control of means provided upwards, i.e. for instance, in the switching node, and in that, in the upward direction, each VP has a fixed bandwidth.
Therefore, it is not necessary to provide the users' equipment (access node or subswitching node) with means controlling the bandwidth. In other words, the users' equipment may be as simple as with the VB5.1 standard, but the invention provides the possibility to modify dynamically the bandwidth of each virtual path.
The equipment for controlling the downward bandwidth is preferably under the control of the network operator and is installed, as mentioned above, for instance, in the switching node. This control equipment is provided with information about the maximum bandwidth of each user, i.e. generally of each virtual path, and about the maximum bandwidth at the interface between the switching node and the access or subscriber node. In fact, the bandwidth of each user is an information which is given at the time of subscription and the bandwidth at the interface between the switching node and all the users' node is a characteristic feature of the switching node.
Therefore, for each downward connection, between the switching node and the users, the control equipment allocates the necessary bandwidth to each user, i.e. to each virtual path, taking into account the maximum bandwidth which may be allocated to each user and the maximum bandwidth of the interface.
It may be also possible to control upstream the bandwidth allocated downstream to each virtual channel. This control may be performed in the following way:
The downstream bandwidth of all VCs routed to a given subscriber is checked and compared with the bandwidth allocated for the interface with that specific user. The downstream bandwidth of all VCs routed to a subswitching node is checked and compared with the bandwidth provided by the interface between the switching node and the subswitching node. By combining these two checks, the downstream traffic will not be congested at the two “bottleneck” points, i.e. switching—subswitching node interface and subscriber's interface.
In order to avoid complex shaping control means in the downward direction, a quality of service, i.e. a priority, is assigned to each virtual channel in this downward direction. In other words, the virtual channels of each virtual path are separated in subsets, each subset having a given quality of service. For instance, a first subset of virtual channels corresponds to CBR (Constant Bit Rate), a second subset to UBR (Unspecified Bit Rate), a third subset to VBR real time and a fourth subset to VBR non real time (VBR means “Variable Bit Rate”).
The allocation of qualities of services between the channels of each virtual path may be permanent or semi permanent. In a semi permanent allocation, the qualities of services of the virtual channels may be modified from time to time, for instance when the user requests a modification of his subscription.
In the upward direction, it may be necessary to provide the user with shaping control means when the user has the possibility to transmit data with different qualities of services, but these shaping means may be relatively simple due to the limited bandwidth allocated upwards. In fact: In order to guarantee the QOS of a connection, the user's source must comply with the established traffic contract and provide shaping at VC level. In the present embodiment, some aggregate shaping may be necessary to comply with the upstream VP bandwidth. This condition may be obtained in a very easy way, by imposing an upstream line rate equal to the upstream VP bandwidth, no dedicated shaper being needed for the aggregate flow.